Conventionally known is a circuit design aiding technology that uses a simulation to judge whether conforming circuits such as static random access memories (SRAMs) are produced at a predetermined chip yield rate.
For example, as one of such technologies, a technology using a worst-case corner is known. In one example using a worst-case corner, parameters in a model function for calculating a circuit performance index are handled as random variables. In other words, in this example, variations in the parameters are taken into account upon performing a simulation. In this example, in a performance index space plotted by these parameters, a point where the performance index takes the maximum value or the minimum value is searched across an equal probability plane corresponding to a predetermined chip yield rate, and the point thus searched is used as a worst-case corner. The parameters at the worst-case corner are then used to judge whether the circuit operates normally in this example.
In such an example, the worst-case corner is determined depending on various conditions such as process conditions P, and a temperature T and a voltage V that are external conditions (hereinafter, abbreviated as PTV conditions). Therefore, when plural sets of different conditions, e.g., PTV conditions, are specified, a worst-case corner is determined for each set of the PTV conditions, and the parameters corresponding to each of the worst-case corners are used in judging whether the circuit operates normally. In such a conventional technology, if the circuit operates normally under all of these condition sets, an examiner considers that conforming circuits can be produced at a predetermined chip yield rate. Related-art examples are described in Japanese Laid-open Patent Publication No. 11-296561, International Publication Pamphlet No. WO 2008/102681, and Y. Tsukamoto et al., “Worst-Case Analysis to Obtain Stable Read/Write DC Margin of High Density 6T-SRAM-Array with Local Vth Variability”, ICCAD 2005, 398-405, 2005.
However, in the conventional technology, because the number of worst-case corners determined increases as the number of condition sets to be simulated increases, the management of the worst-case corners becomes cumbersome.